The present invention relates to pulse generators and in particular to implantable pulse generators that control pacing functions based on sensed events.
The cardiac pacemaker in its simplest form is an electrical circuit in which a battery provides electricity that travels through a conducting wire through the myocardium, stimulating the heart to beat (xe2x80x9ccapturingxe2x80x9d the heart), and back to the battery, thus completing the circuit. Implantable cardiac pacemakers have been in existence since the later 1950""s, although external pacemakers were known even earlier. Since that time great strides have been made in improving upon the leads and the pulse generators that together comprise the pacemaker. In particular, the pulse generator circuitry has evolved from discrete components to semi-custom integrated circuits, which are now fabricated from complimentary metal oxide semi-conductor (CMOS) technology.
As cardiac pacemakers have evolved they have been designed to provide increases in the heart rate for periods when the patient is experiencing physiological stress. These xe2x80x9crate-modulatingxe2x80x9d pacemakers help the patient adapt to physiological stress with an increase in heart rate, even if the patient""s intrinsic heart rate would not allow this to occur. The development of dual-chamber pacemakers has allowed the patient to increase their heart rate if he or she is in sinus rhythm.
The rate-modulated pacemaker has three major components. The first is an indicator, such as for activity, body temperature, or respiratory rate, that provides an approximate measurement of metabolic needs. The second is a sensor that can measure the indicator chosen, such as measurement of body temperature or respiratory rate. The third is a rate controlled algorithm that is in the software of the pacemaker and modulates the pacemaker rate as the sensors send signals to the pacemaker.
As the sensors indicate greater metabolic need, the pacing rate is increased. The rate at which the pacing rate increases, however, is bounded and controlled by a feature called rate smoothing. Rate smoothing is a gradual slowing or speeding of the pacemaker rate based on a percentage of a preceding cardiac interval. This is a mechanism programmed into so types of pacemakers to reduce or to smooth abrupt changes in paced rate, especially at the upper rate limit of dual chamber pacemakers. Conversely, if a patient were to develop an ectopic atrial tachycardia, this programmed feature would cause gradual increase in rate rather than abrupt increase in rate.
Rate smoothing is, however, not always a desirable feature under certain circumstances. For example, when an individual needs rapid cardiac output in a short time, such as in a stressful situation, rate smoothing will prevent the heart rate from rising rapidly enough to keep-up with the individual""s cardiac demands. Similarly, once the stressful situation has passed the individual""s will slow only at the rate dictated by the rate smoothing algorithm. This situation can lead to unnecessary constraints on the heart rate. Also, the pacemaker provides pacing pulses that are unnecessary for the proper functioning of the heart (e.g., wastes battery resources on unnecessary pacing pulses). Thus, a need exists in the art to provide for a more flexible way of utilizing the rate smoothing algorithm.
The present invention provides a system and method for controlling a rate smoothing system in a pulse generating system. In one embodiment, the rate smoothing system is either activated or deactivated (turned on or turned off) when a triggering event is detected. In an alternative embodiment, when a parameter adjusting events is detected parameters of the rate smoothing system are adjusted (e.g., changed). Under either situation (turning on/off or adjustment of parameters) the changes to the rate smoothing system/function are temporary. In one embodiment, the duration of the changes is over a first time interval, after which the rate smoothing system is either set to the original pre-event state or to a state in which one or more of the original parameter values/settings have been changed from the original pre-event state. By allowing selected events to temporarily activate/deactivate or change parameter settings for a rate smoothing system, greater flexibility in treating a patient""s cardiac conditions is achieved as compared to allowing the rate smoothing function to continuously operate. The present subject matter can be used with rate smoothing systems applied to either ventricular pacing or atrial pacing.
In one embodiment, the present system provides monitoring for a trigger signal a parameter adjusting event or both. In one embodiment, the system uses a signal input system, where the signal input system is adapted to detect a signal. Control circuitry coupled to the signal input system receives the signal from the signal input system. In one embodiment, a trigger event detector in the control circuitry receives the signal and analyzes the signal for the occurrence of the trigger event. The trigger event detector is further coupled to a rate smoothing module. In one embodiment, the rate smoothing module executes and controls the rate smoothing algorithm. When the triggering event is detected, the rate smoothing module is then either activated to provide rate smoothing or deactivated to stop rate smoothing, depending upon the state of the module prior to the triggering event. Once the rate smoothing system is activated or deactivated, a timer is used to time a first interval. After the first interval expires, the rate smoothing system is then reset, or restored, to its state prior to the trigger signal. Alternatively, after the first interval expires, the rate smoothing system changes one or more of the original parameter values/settings (i.e., pre-trigger signal parameter state or pre-parameter adjusting event parameter state) to provide a new parameter state. The new parameter state is then used in the rate smoothing system until a subsequent trigger signal and/or parameters adjusting event is detected. A new parameter state can be created after each trigger signal and/or parameters adjusting event (e.g., a sequence of changes to the parameter values and/or settings for the rate smoothing system).
In an alternative embodiment, a parameter adjustment event detector coupled to the control circuity receives the signal from the signal input system. In one embodiment, the parameter adjustment event detector receives and signal and analyzes the signal for the occurrence of a parameter adjustment event in the signal. When the parameter adjustment event is detected, the rate smoothing module adjusts rate smoothing parameters. In one embodiment, the parameters adjusted are the percent change in pacing rate for either up or down rate smoothing.
Any number of detected events are used as either triggering events or parameter adjustment events. For example, triggering events or parameter adjustment events are detected in activity signal sensed using activity monitors such as accelerometers or minute ventilation systems. In this embodiment, an activity signal is monitored from an activity sensor. The triggering event or parameter adjustment event is then detected when the activity signal exceeds a first predetermined value. In an additional embodiment, the activity signal is a heart rate acceleration, where the triggering event or parameter adjustment event is when a heart rate trajectory exceeds the first predetermined value.
In an additional embodiment, triggering events or parameter adjustment events are found in monitored cardiac signals. For example, monitoring for the triggering event or parameter adjustment events includes monitoring a cardiac signal which includes indications of ventricular contractions. The cardiac signal is then analyzed for the occurrence of premature ventricular contractions (PVC). When one or more PVC occur, the triggering event or parameter adjustment event is detected. Alternatively, the cycle length pattern of cardiac cycles detected in the cardiac signal are used as triggering events or parameter adjustment events. For example, a detected short-long-short cycle length sequence from a cardiac signal is a triggering event or parameter adjustment event. Alternatively, the triggering event or parameter adjustment event is when a cardiac rate exceeds a rate threshold. In an additional embodiment, the triggering event or parameter adjustment event occurs after the end of an arrhythmic episode.
In an alternative embodiment, triggering events or parameter adjustment events occur at selected times within a time interval. For example, monitoring for the triggering event or parameter adjustment events includes monitoring a time interval, such as the time of the day, week, month, year or event the season of the year. The triggering event or parameter adjustment event is then detected at a first time in the time interval, where the first time is either programmed by the physician or set based on the implantable systems analysis of one or more detected signals. Alternatively, the triggering event or parameter adjustment event is when a pacemaker mode is changed.